Interface thermal resistance and thermal conductivity in composites – an abrupt junction thermal diode model

An abrupt junction diode model is proposed to study the interface thermal resistance and thermal conductivity of composite. We have demonstrated that the structure of thermal diode greatly influences the heat flow and hence it is possible to regulate the heat flow via the geometry of the diode. The composite materials can significantly reduce the thermal conductivity compared to an equivalent single material. By tuning the mass ratio of oscillator of right segment to that of oscillator of left segment of the composite, _MR/_ML$M_{\mathrm{R}}/M_{\mathrm{L}}$, crossover between negative differential thermal resistance and positive differential thermal resistance as well as figure of merit for composite material can be tuned. It is also seen that the composite will work as a better thermal insulating material than its pure constituent materials.     

Relativistic gravitational collapse by thermal mass

Gravity and thermal energy are universal phenomena which compete over the stabilization of astrophysical systems.The former induces an inward pressure driving collapse and the latter a stabilizing outward pressure generated by random motion and energy dispersion.Since a contracting self-gravitating system is heated up one may wonder why is gravitational collapse not halted in all cases at a sufficient high temperature establishing either a gravo-thermal equilibrium or explosion.Here,based on the equivalence between mass and energy,we show that there always exists a temperature threshold beyond which the gravitation of thermal energy overcomes its stabilizing pressure and the system collapses under the weight of its own heat.     

A piezoresistive micro-cantilever for thermal infrared detector

A novel tri-layer Si-based micro-cantilever thermal infrared (IR) detector with carbon nanotube (CNT) film is fabricated. It is based on the characteristic that the composite micro-cantilever bends in response to incident IR thermal radiation due to the bi-material effect. The bending of micro-cantilever is piezoresistively detected. Furthermore, a new IR absorbing layer material-CNTs-is coated in order to enhance IR radiation absorbing characteristic, the micro-electro-mechanical system (MEMS) sensor could be compatible with integrated circuit technology.     

Cluster-state preparation in thermal cavities without single-qubit operation

A potential scheme is proposed for generating cluster states of many atoms in cavity quantum electradynamics （QED）, in which an unorthodox encoding is employed with the ground state being qubit [0〉 while two closely spaced upper states being qubit ｜1〉. Throughout the scheme the cavities can be in thermal states but axe only virtually excited. We show how to create the cluster states by performing a two-step hut no single-qubit operation. Discussion is also carried out on the experimental feasibility of our scheme.     

Supra—thermal Electron Generation at Moderate Laser Intensity

The effects of re-scattering on the supra-thermal electron (STE) produced in moderate laser fields are analytically considered (laser intensity I is up to 5.0×10¹⁶ W•cm^-2) with a simple model. The electron kinetic energy distribution given by the model is consistent to that given by the particle-in-cell simulation. Based on this fact, it is shown that the scattering of electron in intense laser by the ion in plasma plays an important role in the generation of STE in a moderate laser field.     

The intensity distribution and thermal stability of InnoSlab laser

Partially end-pumped slab laser is an innovative solid state laser, namely InnoSlab. Combining the hybrid resonator with partially end-pumping, the output power can be scaled with high beam quality. In this paper, the output intensity distributions are simulated by coordinate transformation fast Fourier transform (FFT) algorithm, comparing the thermal lens influence. As the simulated curves showed, the output mode is still good when the thermal lens effect is strong, indicating the good thermal stability of InnoSlab laser. Such a new kind of laser can be designed and optimized on the base of this simulation.     

A statistical model for predicting thermal chemical reaction rate

A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 （2011）] or molecules [Chin. Phys. Lett. 29 080504 （2012）] was used to predict chemical reaction rates without empirical parameters, and its physical basis was further investigated both theoretically and via MD simulations. The model was successfully applied to some reactions of extensive experimental data, showing that the model is significantly better than the conventional transition state theory. It is worth noting that the prediction of the model on ab initio level is much easier than the transition state theory or unimolecular RRKM theory.     

Measurement of thermal expansion coefficient of nonuniform temperature specimen

A new technique is developed to measure the longitudinal thermal expansion coefficient of C/C composite material at high temperature.The measuring principle and components of the apparatus are described in detail.The calculation method is derived from the temperature dependence of the therinal expansion coefficient.The apparatus mainly consists of a high temperature environmental chamber,a power circuit of heating,two high-speed pyrometers,and a laser scanning system.A long solid specimen is resistively heated to a steady high-temperature state by a steady electrical current.The temperature profile of the specimen surface is not uniform because of the thermal conduction and radiation.The temperature profile and the total expansion are measured with a high-speed scanning pyrometer and a laser slit scanning measuring system,respectively.The thermal expansion coefficient in a wide temperature range(1000-3800 K)of the specimen can therefore be obtained.The perfect consistency between the present and previous results justifies the validity of this technique.     

Microbending loss and refractive index changes induced by transient thermal loading in double-coated optical fibers with thermal contact resistance

The transient microbending loss and refractive index changes in a double-coated optical fiber subjected to thermal loading with stress-dependent interlayer thermal contact resistance is investigated. The effects of interlayer thermal resistance on the transient microbending loss and refractive index changes of the optical fiber are analyzed and discussed. The results show that the stress-dependent interlayer thermal contact resistance will increase the lateral pressure induced by the transient thermal loading in the double-coated optical fiber and, thus, the microbending loss. Similarly, the interlayer thermal contact resistance will increase the transient thermal loading induced refractive index changes in the beginning of loading.     

α-quartz as a substrate in thermal phonon radiation

Using the mechanical strong anisotropic-quartz, measurements of radiation temperature as a function of phonon radiation power were performed for gold and copper radiators evaporated on theX- orZ-crystal face, respectively. The comparison with theoretical model calculations of phonon transmission across the interface yields agreement with the isotropic/anisotropic acoustic mismatch model. A strong increase in radiation temperature in comparison to linear emission models is observed at temperatures above about 40 K. We suppose that this effect is due to phonon back-scattering which leads to a back-heating of the metal film.Supported by Bundesministerium für Forschung und Technologie     

Size-dependent thermal stresses in the core–shell nanoparticles

The thermal stress in a magnetic core–shell nanoparticle during a thermal process is an important parameter to be known and controlled in the magnetization process of the core–shell system. In this paper we analyze the stress that appears in a core–shell nanoparticle subjected to a cooling process. The external surface temperature of the system, considered in equilibrium at room temperature, is instantly reduced to a target temperature. The thermal evolution of the system in time and the induced stress are studied using an analytical model based on a time-dependent heat conduction equation and a differential displacement equation in the formalism of elastic displacements. The source of internal stress is the difference in contraction between core and shell materials due to the temperature change. The thermal stress decreases in time and is minimized when the system reaches the thermal equilibrium. The radial and azimuthal stress components depend on system geometry, material properties, and initial and final temperatures. The magnitude of the stress changes the magnetic state of the core–shell system. For some materials, the values of the thermal stresses are larger than their specific elastic limits and the materials begin to deform plastically in the cooling process. The presence of the induced anisotropy due to the plastic deformation modifies the magnetic domain structure and the magnetic behavior of the system.     

Measured thermal dissipation field in turbulent Rayleigh-Bénard convection

The time-averaged local thermal dissipation rate epsilonN(r) in turbulent convection is obtained from direct measurements of the temperature gradient vector in a cylindrical cell filled with water. It is found that epsilonN(r) contains two contributions. One is generated by thermal plumes, present mainly in the plume-dominated bulk region, and decreases with increasing Rayleigh number Ra. The other contribution comes from the mean temperature gradient, being concentrated in the thermal boundary layers, and increases with Ra. The experiment thus provides a new physical picture about the thermal dissipation field in turbulent convection.     

A novel two-dimensional thermal convection based MEMS acoustic vector sensor

An acoustic vector sensor can measure acoustic particle velocity and pressure simultaneously,which is important for capturing sound field information.An integrated twodimensional(2D) vector sensor is desired for various applications;however,its manufacturing remains challenging.In this study,a novel thermal-convection-based acoustic vector sensor comprising multiple crossed wires suspended in an etched cavity is designed.The sensor can directly measure two-dimensional particle velocity,and its p...     

How fundamental is the character of thermal uncertainty relations?

We discuss here two different information measures of the Tsallis type, and their associated probability distributions, in order to repeat the Mandelbrot Cramer–Rao steps that lead to a thermal uncertainty relation for exponential distributions. We deal first with the original Tsallis measure and discuss afterwards a second entropic measure associated with the concept of escort distribution. In neither case it is possible to re-obtain a thermal uncertainty relationship. We conclude therefore that the thermal uncertainty, as derived from the Cramer–Rao inequality, cannot be as fundamental as the quantum one.     

How does the EAS look like in thermal neutrons?

The first experimental data on detection of thermal neutrons accompanying extensive air showers (EASs) which were obtained at two prototypes of the future novel PRISMA EAS array are reported. The operation of this array (even in the minimum prototype version) and its ability to yield completely new information on the hadron and electron components of the EAS were experimentally checked.     

Design of the thermal neutron detection system for CJPL-Ⅱ

A low background thermal neutron flux detection system has been designed to measure the ambient thermal neutron flux of the second phase of the China Jinping Underground Laboratory(CJPL-Ⅱ),right after completion of the rock bolting work.A ~3He proportional counter tube combined with an identical ~4He proportional counter tube was employed as the thermal neutron detector,which has been optimised in energy resolution,wall effect and radioactivity of construction materials for low background performance.The readout electronics were specially designed for long-term stable operation and easy maintenance in an underground laboratory under construction.The system was installed in Lab Hall No.3 of CJPL-Ⅱ and accumulated data for about 80 days.The ambient thermal neutron flux was determined under the assumption that the neutron field is fully thermalized,uniform and isotropic at the measurement position.     

Design and fabrication of GeAsSeS chalcogenide waveguides with thermal annealing

We reported a chalcogenide glass-based rib waveguide fabricated using photolithography and dry etching method. A commercial software(COMSOL Multiphysics) was used to optimize the waveguide structure and the distribution of the fundamental modes in the waveguide based on the complete vector finite component. We further employed thermal annealing to optimize the surface and sidewalls of the rib waveguides. It was found that the optimal annealing temperature for Ge As Se S films is 220℃, and the roughness of the films could be significantly reduced by annealing. The zero-dispersion wavelength(ZDW) could be shifted to a short wavelength around ~2.1 μm via waveguide structural optimization, which promotes supercontinuum generation with a short wavelength pump laser source. The insertion loss of the waveguides with cross-sectional areas of 4.0 μm×3.5 μm and 6.0 μm×3.5 μm was measured using lens fiber and the cut-back method. The propagation loss of the 220℃ annealed waveguides could be as low as 1.9 d B/cm at 1550 nm.